Five cycle engines of the type herein contemplated have been proposed in the patented literature for more than sixty-eight years. The Packard Motor Car Co. was granted U.S. Pat. No. 1,788,140, on Jan. 6, 1931, which discloses the basic five cycle engine herein contemplated.
The '140 patent discloses an internal combustion engine comprising a housing, a plurality of annularly arranged cylinders in the housing disposed with their axes parallel with a central longitudinal rotor axis. Each of the cylinders includes an inlet end portion having an inlet port therein, a central working portion, and an outlet end portion having an outlet port therein. An inlet piston is mounted in each cylinder constructed and arranged to be moved in sealing relation to the associated cylinder from an inlet end position wherein the inlet port thereof communicates with the working portion thereof in an axial direction away from the inlet end position into an inlet port cut-off position wherein the inlet piston cuts off communication of the inlet port thereof with the working portion thereof and beyond into the working portion thereof. An outlet piston is mounted in each cylinder constructed and arranged to be moved in sealing relation to the associated cylinder from an outlet end position thereof wherein the outlet port thereof is communicated with the working portion thereof in an axial direction away from the outlet end position into an outlet port cut-off position wherein the outlet piston cuts off the communication of the outlet port thereof with the working portion thereof and beyond into the working portion thereof. Rotor structure within the housing is constructed and arranged to move with a rotational movement within the housing about the central rotor axis. Each of the inlet pistons includes an inlet cam follower constructed and arranged to follow an annular inlet cam during the rotation of the rotor structure. Each of the outlet pistons includes an outlet cam follower constructed and arranged to follow an annular outlet cam during the rotation of the rotor structure. The inlet and outlet annular cams are configured to move the inlet and outlet pistons within each cylinder through a successive five-cycle repeating movement which includes (1) a power cycle wherein the inlet and outlet pistons are moved axially outwardly from combustion positions disposed in closely spaced relation within the working portion of the associated cylinder into the respective cut-off positions thereof, (2) an exhaust cycle wherein the outlet piston is moved from the outlet cut-off position thereof into the outlet end position thereof and the inlet piston is moved through the working portion thereof into close proximity to the outlet piston, (3) a transfer cycle wherein the inlet and outlet pistons are moved together in close proximity to each other through the working portion thereof, (4) an intake cycle wherein the outlet piston is initially moved through the working portion of the associated cylinder while the inlet piston is in a position allowing communication of the inlet port with the working portion with the final movement of the intake cycle resulting in the inlet and outlet pistons being in compression positions spaced from the respective end positions thereof so that the communication of the respective ports are cut off from the working portion of the associated cylinder, and (5) a compression cycle wherein the inlet and outlet pistons are moved from the compression positions thereof toward each other into the combustion positions.
The '140 patent disclosure contemplates that the compression positions of the inlet and outlet pistons in the intake cycle constitute the respective cut-off positions thereof, both of which are moved directly therein during the final movements of the intake cycle. In this way, a maximum power is achieved and opposed piston movement balance is achieved during the full movement of the opposed pistons during compression as well as during expansion.
It is noted, however, that the transfer cycle introduces an imbalance because both pistons are moved together through a full stroke. Similarly, the intake and exhaust cycles involve different movements of the pistons in the same direction.
Over the years, there have been various improvements on the basic five-cycle engine proposed in the patented literature. The Packard Motor Car Co. was granted improvement U.S. Pat. No. 1,808,083, contemporaneously with the basic '140 patent on Jun. 2, 1931. This Packard improvement was directed toward diminishing the imbalanced movement of the pistons together during the transfer cycle by essentially halving the movement required and doubling the five cycle operation to a ten cycle operation.
U.S. Pat. No. 5,289,802 introduced two features of improvement in the basic five-cycle operation. First, an increased compression-expansion ratio beyond one is proposed where the compression positions of the inlet and outlet pistons in the intake cycle constitute the cut-off position of the inlet piston and an intermediate position of the outlet piston disposed inwardly of the outlet cut-off position thereof, both of which are moved directly therein during the final movements of the intake cycle. The intake cycle is essentially accomplished by a movement of the outlet piston within the cylinder which positively displaces a new charge through the open inlet port. Second, the inlet and outlet annular cams retain the inlet and outlet pistons substantially in combustion positions longer than simple harmonic motion for a time sufficient to enable a new fueled gas charge within the minimum column to be ignited and to rise to maximum pressure before substantial volume increase toward the maximum volume during the power cycle takes place to thereby eliminate negative work resulting from ignition prior to reaching the minimum volume condition and to obtain optimal work from optimal pressure conditions.
While these improvements to some extent have a positive effect on the inherent imbalance of the basic five-cycle movement, it is apparent that the problem of inherent imbalance has gone unsolved since 1931 despite the various improvements which have been proposed over the years.